This application proposes to establish a Hepatitis C Cooperative Research Center at University of Southern California (USC) to coordinate and advance research on the pathogenesis and persistency of hepatitis C virus (HCV). HCV has become the major cause of chronic hepatitis in this country. Very few options for therapeutic intervention and prevention are available. This proposed center will facilitate and expand their long-standing collaborative research activities at USC. Four specific projects are proposed: (1) Studies of HCV core protein and host defense, based on the findings made by the P.I.'s laboratory that HCV core protein interacts with tumor necrosis factor (TNF) receptors. This project will examine the biochemical properties of this interaction and their biological consequences. It also proposes to establish an in vitro cell culture system for HCV replication. (2) Establishment of a transgenic mouse model for studying HCV pathogenesis. We will characterize transgenic mice expressing HCV core protein, and use cytotoxic T cells to attempt to induce hepatitis. This model will be used to determine whether the core protein expression in immune cells can alter the immune functions and the responses to cytokines. This project will address the role of hepatic and extrahepatic infection in HCV pathogenesis. (3) Studies of the molecular biology of core protein and RNA replication. This project will examine the biochemistry and biological functions of various forms of HCV core protein. It will also establish an RNA transfection assay to examine the RNA sequence requirement for HCV RNA replication. (4) Study of molecular and clinical parameters of HCV infection during therapies and in the presence of co-infection with human immunodeficiency viruses (HIV). Hepatitis C patients who have received ribavirin or interferon therapies will be studied with respect to TNF receptors, HCV viral antigen expression and other cytokines during and after therapy to attempt to demonstrate a correlation between these parameters and liver pathology. Patients with HCV and HIV infections will be compared with those with HCV infections only. These studies are expected to provide an understanding of the molecular basis of the mechanism of liver injury and the effects of various therapies in humans. Taken together, these projects utilize the unique resources at the USC medical campus, which include expertise in virology, molecular biology, and immunology of HCV, as well as large patient populations. These studies are expected to contribute to the understanding of viral pathogenesis and persistent infection.